1. Field of the Invention
The present invention relates to a color diffusion transfer photographic process, more particularly, to a photographic material adapted for obtaining stable transferred color images by a color diffusion photographic process.
2. Description of the Prior Art
In general, a color diffusion transfer photographic light-sensitive material (hereinafter referred to as "DTR color light-sensitive material") comprises (1) a light-sensitive element having three units (corresponding to the three primary colors) each of which contains a dye-providing material capable of providing a diffusible dye, and a light-sensitive silver halide emulsion layer in combination; (2) a processing element containing a processing solution composition (alkaline aqueous solution or aqueous dispersion) capable of developing exposed light-sensitive elements and permitting dyes to diffuse; and (3) an image-receiving element containing an image-receiving layer capable of image-wise fixing diffused dyes.
One merit of DTR color light-sensitive materials is that color print photographic picture can be obtained immediately after photography, and, in order to maximally utilize this benefit, an "instant photographic processing" mechanism, in which stabilizing processings such as washing of images or fixing images after development processing are not involved, is incorporated in a light-sensitive material, which is quite different from conventional photographic processes.
Since washing or fixing processing are not per se conducted as separate steps in diffusion transfer photographic processing, it is necessary to provide in a light-sensitive material some mechanism to automatically stabilize images in order to obtain stable images.
As one process for stabilizing images, it is known to provide a neutralizing mechanism in a light-sensitive material, that is, to remove those factors which destroy or change formed images by absorbing, after development processing, alkali ingredients and salt-forming reagents in a processing solution.
U.S. Pat. Nos. 3,362,819 and 3,575,701 suggest some techniques for this purpose, which fundamentally comprise providing on a support an acidic polymer layer and an inert polymer layer (hereinafter referred to as a "timing layer"). The acidic polymer layer functions to absorb alkali ingredients and salt-forming reagents in the processing solution, whereas the timing layer functions to delay the initiation of the function of the acidic polymer (layer) in order to prevent too early an initiation of the function of the acidic polymer (layer), which would result in insufficient developing.
As the inert polymer (timing layer), the aforesaid U.S. Patents describe polymers such as polyvinyl alcohol, partially acetallized products thereof, gelatin, polyvinylamide graft copolymers, and the like. The neutralizing mechanism involving these polymers comprises transmitting almost constant amounts of water, alkali ingredients and salt-forming reagents during development, and, as a result, possesses the characteristic that pH is comparatively rapidly decreased in an image-receiving layer and a light-sensitive layer.
Such a rapid pH decrease fails to maintain the pH at a level necessary for development, and, as a result, the particularly desired rapid developing velocity cannot be obtained. On the other hand, when pH decreases comparatively slowly, it takes a comparatively long period of time for the pH value to reach a region where images are stable (pH 5 to 7, preferably 6 to 7). Thus, there is the defect of probable staining (or spoiled image stability).